Summary
Five lactose-specific lectins from snake venoms were tested for the ability to stimulate
the aggregation of human platelets. Three of the lectins, bushmaster (Lachesis muta), cottonmouth (Aricistrodon piscivorous leukostoma) and rattlesnake (Crotalus atrox) lectins, consistently stimulated secretion and aggregation. Thrombolectin (Bothrops atrox) occasionally caused aggregation. Copperhead (Agkistrodon contortrix contortrix) lectin did not by itself cause platelet aggregation. Lactose, a specific inhibitor
of hemagglutination mediated by these lectins was a potent inhibitor of lectin-induced
aggregation. Antiserum specific for bushmaster lectin inhibited aggregation by bushmaster
lectin. In contrast, the same antiserum and anti-cottonmouth lectin serum enhanced
aggregation by low levels of the other lectins.
A variety of substances were assayed in the aggregometer for the ability to inhibit
aggregation in response to these lectins. Both secretion and aggregation were inhibited
by PGI2 and PGEx. Furthermore, lectin-induced aggregation was completely blocked by trifluoperazine
and partially blocked by indomethacin. Monoclonal antibodies specific for GP IIb/IIIa
(AP2, A2A9, LJP5, LJCP8) but not monoclonals directed against other platelet membrane
proteins (API and AP3) inhibited lectin-induced aggregation. The peptide Arg-Gly-Asp-Ser
but not Arg-Ala-Asp-Ser was a potent inhibitor of aggregation.
Keywords
Snake venom - Lactose-inhibitable lectins - Platelets Summary